China is blocking mention of Inner Mongolia on Chinese microblogs and social networking sites, as part of an effort to clamp down on protests that broke out last week in the region.

Two of the most popular microblog services operating in China no longer allow users to search for the term "Inner Mongolia." Sina's and Tencent's microblogs have 140 million and 160 million users, respectively.

Social networking site Renren, nicknamed "Facebook of China", is also preventing users from posting about "Inner Mongolia." Renren users who have registered China's Inner Mongolia region as their hometown also reported that their friends cannot fully view their user pages.

The censorship comes after protests erupted in the region when an ethnic Mongolian shepherd was run over by an ethnic Han truck driver, according to human rights groups. Ethnic Mongolians in the region have taken to the streets, prompting authorities to declare martial law in some of the cities.

The Southern Mongolian Human Rights Information Center said on its website that China's most popular instant messenger service QQ, which helped organize the mass protests, has been shutdown in the region.

The Inner Mongolia region of China borders Mongolia and has a population of 24 million people. Only 17 percent of the region's population is Mongolian. About 78 percent of the population are from the country's main ethnic Han group.

China has 457 million Web users, according to the China Internet Network Information Center. But the country regularly blocks politically sensitive content on the Web. Internet censorship has ramped up to new levels starting this year, according to experts. It was triggered by an online protest call urging Chinese people to stage a "Jasmine Revolution" against the government.

China responded by blocking any mention of the term "Jasmine" on Chinese microblogs. Google also reported that Chinese authorities were blocking Gmail, in what experts said was an effort to stifle communication between human rights activists.